1. Field of the Invention
The present invention relates generally to the field of oxygen scavenging compositions. More particularly, it concerns oxygen scavenging compositions comprising non-fragmenting oxygen scavenging polymers.
2. Description of Related Art
Organic polymers have made significant inroads into the packaging industry due to their design flexibility and the ability to be fabricated in various sizes and shapes commonly used in the packaging industry. The deployment of organic polymers into films, bottles, coatings, and liners is commonplace in the packaging industry. Although plastic materials offer the packaging industry many benefits, the application of plastic materials has remained inhibited in situations where there are special packaging requirements to prevent the ingress of exterior oxygen or to scavenge oxygen present inside the package. In some cases, particularly in the fruit juice and brewing industries, oxygen is removed from the product by vacuum, inert gas sparging, or both. However, it is difficult and expensive to remove the last traces of oxygen by these techniques, along with an additional disadvantage of tending to remove volatile aroma and flavor components in the products.
Another, more recent, technique for limiting oxygen exposure of packaged food products involves incorporating an oxygen scavenger into the packaging structure. One important class of oxygen scavengers is oxygen scavenging polymers. Oxygen scavenging polymers, in the presence of a suitable oxidation catalyst, scavenge (i.e., react irreversibly) with oxygen from either the inside of the package or ingressed from the exterior of the package. There have been extensive developments of oxygen scavenging technology in both flexible and rigid packaging application.
Depending on the type of application, there can be considered to be two categories of oxygen scavenging polymers. The first one is based on unsaturated addition polymers, such as polybutadiene or polyisoprene, which undergoes an allylic oxidation pathway in consuming oxygen. This type of oxygen scavenging polymer has demonstrated sufficient oxygen scavenging capability in flexible packaging structures, but the odor and taste alteration remains a concern for further commercial applications. For rigid packaging applications, polyolefin-based oxygen scavenging polymers suffer from the incompatibility with those polymers typically used in rigid packaging application, such as PET or nylon, among others. This includes physical incompatibility, which leads to loss of clarity critical for many rigid packaging applications, and incompatible processing due to the thermal stability of the polyolefin-based oxygen scavenging polymers in the temperature range typically used for processing rigid packaging polymers, such as PET.
The second category, of which MXD6 polyamide has been the only example, undergoes oxidation through xe2x80x94Phxe2x80x94CH2xe2x80x94NHxe2x80x94 linkage on the polymer backbone. MXD6 polyamide has been demonstrated to improve oxygen barrier performance by scavenging the ingress of exterior oxygen into the bottle or container. However, the breakdown of the polymer chain and the generated by-products, such as aldehyde and acid volatile components, have limited the application of MXD6, especially in situations where direct food contact is required. The minimization or elimination of fragmentation of oxygen scavenging polymers has been a major challenge since the early development of this technology field. Thus, in spite of a long-recognized need and the large size of the potential market in the rigid packaging, it remains desirable to have oxygen scavenging polymers that do not generate fragments upon reaction with oxygen, and at the same time can withstand stringent process/fabrication processing conditions.
In one embodiment, the present invention relates to an oxygen scavenging composition, comprising:
an oxygen scavenging polymer comprising units having structure I: 
xe2x80x83wherein R1 and R2 are independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94NHC(xe2x95x90O)xe2x80x94, xe2x80x94NHC(xe2x95x90O)Oxe2x80x94, and xe2x80x94NRxe2x80x94, wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls;
a transition metal oxidation catalyst; and
a photoinitiator having a wavelength of maximum absorption of electromagnetic radiation from about 200 nm to about 750 nm.
In another embodiment, the present invention relates to an oxygen scavenging composition, comprising:
an oxygen scavenging polymer comprising units having structure I, as described above, wherein R1 and R2 are independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94NHC(xe2x95x90O)xe2x80x94, xe2x80x94NHC(xe2x95x90O)Oxe2x80x94, and xe2x80x94NRxe2x80x94, wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls;
a transition metal oxidation catalyst; and
a microwave reactive material.
In still another embodiment, the present invention relates to an oxygen scavenging packaging article, comprising an oxygen scavenging layer comprising:
an oxygen scavenging polymer comprising units having structure I, as described above, wherein R1 and R2 are independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94NHC(xe2x95x90O)xe2x80x94, xe2x80x94NHC(xe2x95x90O)Oxe2x80x94, and xe2x80x94NRxe2x80x94, wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls;
a transition metal oxidation catalyst; and
an energy-absorbing compound selected from the group consisting of microwave reactive materials and photoinitiators having a wavelength of maximum absorption of electromagnetic radiation from about 200 nm to about 750 nm.
In yet another embodiment, the present invention relates to a method of initiating oxygen scavenging by an oxygen scavenging composition, comprising:
(a) providing an oxygen scavenging composition, comprising:
(i) an oxygen scavenging polymer comprising units having structure I, as described above, wherein R1 and R2 are independently selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94NHC(xe2x95x90O)xe2x80x94, xe2x80x94NHC(xe2x95x90O)Oxe2x80x94, and xe2x80x94NRxe2x80x94, wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls;
(ii) a transition metal oxidation catalyst; and
(iii) an energy-absorbing compound selected from the group consisting of microwave reactive materials and photoinitiators having a wavelength of maximum absorption of electromagnetic radiation from about 200 nm to about 750 nm; and
(b) exposing the oxygen scavenging composition to electromagnetic radiation for a duration sufficient to initiate oxygen scavenging by the oxygen scavenging composition.
In still another embodiment, the present invention relates to a method of forming a polymer, comprising:
providing at least a monomer having structure IV: 
xe2x80x83wherein R5 and R6 are independently selected from the group consisting of xe2x80x94OH, xe2x80x94OR, xe2x80x94C(xe2x95x90O)OH, xe2x80x94C(xe2x95x90O)OR, xe2x80x94NH2, xe2x80x94NHR, xe2x80x94NR2, xe2x80x94NHC(xe2x95x90O)H, xe2x80x94NHC(xe2x95x90O)R, xe2x80x94NHC(xe2x95x90O)OH, and xe2x80x94NHC(xe2x95x90O)OR, wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls; and a monomer having structure VI:
xe2x80x83R7xe2x80x94Xxe2x80x94R8xe2x80x83xe2x80x83(VI)
xe2x80x83wherein X is a hydrocarbon or substituted hydrocarbon; and R7 and R8 are selected from the group consisting of xe2x80x94OH, xe2x80x94OR, xe2x80x94C(xe2x95x90O)OH, xe2x80x94C(xe2x95x90O)OR, xe2x80x94NH2, xe2x80x94NHR, xe2x80x94NR2, xe2x80x94NHC(xe2x95x90O)H, xe2x80x94NHC(xe2x95x90O)R, xe2x80x94NHC(xe2x95x90O)OH, xe2x80x94NHC(xe2x95x90O)OR, and -halide; wherein R is selected from the group consisting of xe2x80x94H and xe2x80x94C1-C6 alkyls; and condensation polymerizing at least the monomer having structure IV and the monomer having structure VI, to form the polymer.
In yet a further embodiment, the present invention relates to a method of producing a packaging article comprising an oxygen scavenging layer, wherein the oxygen scavenging layer comprises a polymer comprising structure I: 
wherein R1 is selected from the group consisting of xe2x80x94Oxe2x80x94 and xe2x80x94NHxe2x80x94, and R2 is selected from the group consisting of xe2x80x94Oxe2x80x94 and xe2x80x94NHxe2x80x94, the method comprising:
providing a composition comprising the polymer comprising structure I, and
forming the composition into a packaging article or an oxygen scavenging layer thereof.
The present invention provides an oxygen scavenging composition, and packaging articles comprising oxygen scavenging layers comprising the oxygen scavenging composition, which do not generate fragments upon reaction with oxygen.